1. Field of the Invention
The present invention relates to chiral cheating agents and chiral catlysts, wherein the chiral catlysts are formed from the chiral chelating agents and metals.
2. Background of the Invention
The use of catalytic asymmetric reactions for the synthesis of enantiomerically pure compounds has been an ongoing effort of organic chemists. The coupling of an α,β-unsaturated carbonyl/nitrile with an aldehyde (Morita-Baylis Hillman reaction) produces a useful functionalized acrylate that allows for further functional group manipulation. The reaction can be catalyzed by using a chiral catalyst to synthetize a product having high level of enantiomeric excess. The mechanism of the Baylis-Hillman reaction, which is mediated by a tertiary amine, is illustrated as follows: Although the diastereoselective Baylis-Hillman reaction has been shown to proceed, in some cases, with high to excellent diastereoselectivities, the enantioselective variation of this reaction is less well developed.
Recently, Hatakeyama et al. reported that a high to excellent enantiomeric excess can be achieved when quinidine derivatives are used as chiral amine catalysts (J. Am. Chem. Soc., 1999, 121, 10219). The use of a chiral Lewis acid to catalyze this transformation is a common strategy. Aggarwal and co-workers report on the use of lanthanides and group III metal triflates to accelerate the Baylis-Hillman reaction (J. Org. Chem. 1998, 63, 7183 and J Chem. Soc. Chem. Commun., 1996, 2713). However, only 5% ee was obtained, when these metals are complexed with a broad range of oxygen-rich chiral ligands. No practical levels of enantioselectivity have yet been reported when a chiral Lewis acid catalyst is used.